Field of the Invention
The present invention relates to a semiconductor phosphor nanoparticle, a semiconductor phosphor nanoparticle containing glass, a light emitting device, and a light emitting element.
Description of the Background Art
It is known that when a semiconductor nanoparticle is reduced in size to about an excitonic Bohr-radius, it presents a quantum size effect. The quantum size effect is that when a substance is reduced in size an electron in the substance cannot move freely and the electron's energy is not arbitrary and can only assume a particular value. Furthermore, it is known that as the semiconductor nanoparticle, which confines an electron, varies in size, the electron's energy state also varies, and the semiconductor nanoparticle smaller in dimension generates light shorter in wavelength. The semiconductor nanoparticle which presents such a quantum size effect attracts attention for its use as a phosphor and is further researched.
A semiconductor phosphor nanoparticle has high surface activity and accordingly easily aggregates. Accordingly, in order to prevent the aggregation, a method of modifying the nanoparticle's surface with a protective material such as an organic modifying group, is proposed.
Japanese National Patent Publication No. 2010-535262 describes that a modifying group having a carboxylate group and a straight chain alkyl group is used to modify a nanoparticle's surface to obtain a semiconductor phosphor nanoparticle having satisfactory dispersibility in an organic solvent and also having satisfactory fluorescent quantum efficiency.
A semiconductor phosphor nanoparticle normally has a surface with many defects, which serve as a cause of non-radiation deactivation. Since a semiconductor phosphor nanoparticle has a large ratio of surface area to volume per particle and the defects have a large effect on reduction in emission efficiency. Accordingly, a method of enhancing a semiconductor phosphor nanoparticle's emission efficiency by deactivating surface defects, is proposed.
As a first method is indicated coating a surface of a semiconductor nanoparticle with another semiconductor having a large band gap. According to this method, however, a difference in lattice constant between the semiconductors having different band gaps causes distortion in an interface and hence impaired emission characteristics.
As a second method is indicated bonding an organic surfactant to a surface of the semiconductor nanoparticle. According to this method, however, the defects of the surface of the semiconductor nanoparticle cannot all be coated due to a steric hindrance of organic surfactants.
Furthermore, a semiconductor phosphor nanoparticle synthesized in a solution has particles gradually aggregated or the like immediately after it is synthesized, and the semiconductor phosphor nanoparticle thus has degraded emission characteristics, and in particular, a nanoparticle synthesized in a non-aqueous solution is weak against moisture, and is rapidly declined in fluorescence by coexistence of a small amount of moisture, and furthermore, in the form of a solution of nanoparticles, it is difficult to apply it in engineering as a material.
Japanese Patent Laying-Open No. 2007-161748 discloses a method to stabilize a phosphor by coating a surface thereof with a covalently bonded organic thin film.